In the formation of integrated circuits (IC's), thin films containing metal elements are often deposited upon the surface of a substrate, such as a semiconductor wafer. Thin films are deposited to provide conducting and ohmic contacts in the circuits and between the various devices of an IC. For example, a desired thin film might be applied to the exposed surface of a contact or via hole on a semiconductor wafer, with the film passing through the insulative layers on the wafer to provide plugs of conductive material for the purpose of making interconnections across the insulating layers.
One well known process for depositing thin metal films is chemical vapor deposition (CVD) in which a thin film is deposited using chemical reactions between various deposition or reactant gases at the surface of the substrate. In CVD, reactant gases are pumped into proximity with a substrate inside a reaction chamber, and the gases subsequently react at the substrate surface resulting in one or more reaction by-products which form a film on the substrate surface. Any by-products remaining after the deposition are removed from the chamber. While CVD is a useful technique for depositing films, many of the traditional CVD processes are basically thermal processes and require temperatures in excess of 500 or 1000.degree. C. in order to obtain the necessary reactions. Such a deposition temperature is often far too high to be practically useful in IC fabrication due to the effects that high temperatures have on various other aspects and layers of the electrical devices making up the IC. For this reason, one approach which has been utilized in CVD processes to lower the reaction temperature is to ionize one or more of the reactant gases. Such a technique is generally referred to as plasma enhanced chemical vapor deposition (PECVD). An efficient PECVD method has been set forth in commonly assigned U.S. Pat. No. 5,975,912 entitled "Low Temperature Plasma-Enhanced Formation of Integrated Circuits", expressly incorporated by reference herein in its entirety. The '912 patent discloses a method for single-chamber processing of low temperature (&lt;500.degree. C.) PECVD-Ti and TiN films for via applications. U.S. Pat. Nos. 5,567,243 and 5,716,870, each incorporated by reference herein in their entirety, describe hardware design and method for deposition of PECVD-Ti films.
In many applications, a titanium nitride barrier layer is required prior to deposition of certain metal conductors such as aluminum or tungsten. Titanium nitride can be deposited by chemical vapor deposition. The reactants and byproducts of the chemical vapor deposition--in particular, titanium tetrachloride--act to etch the titanium contact layer. Therefore, the titanium must be nitrided prior to titanium nitride chemical vapor deposition. A stack is thus created that includes a titanium film, a nitrided layer of the titanium film and an overlying titanium nitride layer, all between the underlying substrate or conductor and the metal of an overlying layer.
Customary methods of applying and nitriding titanium have been by PECVD. Deposition of titanium nitride has been customarily by thermal CVD. These PECVD and thermal CVD reactions have involved different process parameters, which have called for different processing equipment. As a result, the typical Ti, nitrided Ti and TiN stack production process sequence is performed in two separate modules, often both connected to a common vacuum transfer module of a semiconductor wafer processing cluster tool. The process sequence includes a substantial amount of overhead time for transferring each of the wafers first into a PECVD module and establishing stable process conditions in the module for Ti-PECVD, then after Ti deposition and nitriding of the deposited Ti layer, pumping the module and transferring the wafer through the transfer module to the thermal CVD module for deposition of the TiN layer including establishing stable process conditions in the module for the thermal CVD-TiN deposition, then the removal of the wafer from the thermal CVD-TiN module.
Differing process parameters have prevented integration of PECVD-Ti and thermal CVD-TiN processes in the same module. Traditionally, showerhead temperature for PECVD-Ti are at least 425.degree. C., because lower temperature will form a TiCl.sub.x H.sub.y film which will readily peel off of the showerhead, but not more than 500.degree. C., because higher temperatures will result in chlorine corrosion of metal showerheads that are preferred for plasma generation, temperature control and other reasons in the PECVD reactor. On the other hand, in the thermal CVD reactors used for TiN deposition, showerhead temperature is usually at least 150.degree. C., since lower temperature will cause NH.sub.4 Cl condensation, and not more than 250.degree. C., since higher temperature will produce TiN deposition on the showerhead. Wafer temperatures and chamber pressures are also commonly different for the PECVD-Ti and thermal-CVD reactions. Cycling of temperatures and pressures causes excessive flaking of deposits from reactor components, requiring frequent in-situ and ex-situ cleaning, all of which decreases productivity and increases overhead time, particularly stabilization time to recover from process parameter changes.
Depositions of Ti and TiN in the same reactor have been proposed by using PECVD processes for the TiN deposition as well as the Ti deposition, but TiN film properties and deposition efficiency that are produced with thermal CVD of TiN have had advantages which are preferred.
Accordingly, there is a need for a more efficient and effective method of depositing stacks of Ti, nitrided Ti and TiN, and particularly using PECVD-Ti and thermal CVD-TiN processes.